Electrode for vapor gas electric devices



March 28, 1933. w. T. ANDERSON JR ELECTRODE FOR VAPOR GAS ELECTRIC DEVICE Filed March 8, 1952 INVENTOR; 9 A

ATTORNEY.

Patented Mar. 28, 1933 UNITED STATES WILLIAM 11 ANDERSON,

CHEMICAL AND MANUFACTURING COMPANY,

POBATION or NEW JERSEY ELECTRODE son VAPOR Application filed March a,

This invention relates to electrodes for vapor gas electric devices. These electrodes ma y be employed on the fanuhanforms of mer-ury arcs, both vacuum and gas hlled type,

U for the production of light and for rectificalion, and they may be used for gas discharge tubes for the production of light.

The invention covered by this application is generally described and shown, but not claimed. in Letters Patent No. 1,890,920 issued Dec. 13 1932. on an application filed June 10, 1931, by myself and Hugh 1). Fraser.

Mv invention relates in particular to temperature control (if electron emitting elec- 15 trodes and in order that the importance. and

significance of such control may be thoroughlv understood, it is necessary to describe the conditions existing in and at the. electrodes, of mercury arcs and gas discharge tubes.

The electrode of an air-cooled quartz mer- '-eury vapor arc, which is a familiar article of commerce. consists of a quartz vessel containing mercury corinected to the outside current supply by means of a vacuum sealed lead-in wire. The are discharge is from the surface of the'mercurv. The are possesses a negative volt-ampere characteristic, that is, the. cur- .rent decreases as the voltage increases, and is not to be confused with a high electron disch arge which has a positive'volt-ampere characteristic resulting in high voltage and low amperage. The typical are which will be described operates at 300 watts and 4.2 amperes in the arc itself.

The electron emission and the mercury vapor which maintain the are result from the temperature produced at the. vapor discharge metallic mercury interface. The initial high '40 temperature that starts the are is created by short circuitingthe mercury electrode to the other cl .etrode which may be mercury or some other substance. The area of the vapor discharge 'metallic mercury interface is very small. being about 0.0012 square centimeter for the 4 ampere arc. (For a 20 ampere are it would be about 0.005 square centimeter.) The temperature at this discharge to mercury contact is about 2270 degrees centigrado, at the best operating conditions. The vapor- J'R., 0F NEWARK, NEW JERSEY, ASSIGNOR '10. HANOVIA.

OF NEWARK, NEW JERSEY, A COR- GAS ELEc'rRIq DEVICES 1932. Serial No. 597,461.

. vapor is also condensing in the cooler parts of the container, liberating heat. Finally an equilibrium is established, the final temperature of the. system depending upon the current, radiation and thermal conductance.

Efiicicnt operation demands that this equilibrium temperature be restricted to within certain rather narrow limits. It is characteristic of the mercury are that when the temperature is lowered, the amperage of the arc increases, and vice versa, an increase ,in temperature results in a decrease in amperage. If the temperature be lowered to too great an extent, the high resulting amperage will result in rapid deterioration of the glass or quartz container. On the other hand, if the temperature be increased too much, the amper-age may become too low-to maintain the hot spot, and the arc will be extinguished. Between these two points the are may be operated with various degrees of efliciency.

Temperature in commercial arcs is controlled by limitation of arc current, radio.- tion and provision for adequate electrode cooling surfaces. The electrode surface employed with this typical 300 ,wattair cooled mercury arc has a surface area of about 437 5 square millimeters and contains a volume of mercury about 21,980 cubic millimeters, representing in weight about 300 grams of mercury. This surface may be cooled by natural air convection currents, or the air cooling may be assisted by metal cooling vanes;

I ha e found that the size a d design these mercury electrodes is dependent in a large measure on the low thermal conductivity of metallicmercury. Mercury in a layer one centimeter deep and an area one square centimeter transmits only 0.019 calorie per.

szs

second for an increase in temperature of one degree centigrade. Under similar conditions copper transmits 1.00 calorie per second, aluminum 0.50 calorie per second, tungsten 0.48 calorie persecond, molybdenum 0.34 calorie per second. Thus the thermal conductivity of copper is about 50 times higher than that of mercury.

7 Asa result of this low thermal conductivity, the temperature gradient within the mercury electrode is very great, and hence a -correspondingly greater volume of mercury and a greater surface area are required than would be necessary if the electrode contained, for instance, copper instead of mercury.

It is an object of the invention to provide mercury electrodes which compensate for the low thermal conductivity of the mercury metal, and which are equal in efficiency or better than those familiar to commerce, much smaller in size and volume. The decrease in size and volume has resulted in ,a

- saving in mercury which in the final highly purified form required for use in such arcs is one of the most costly items employed in the manufacture of these arcs. Also, if the envelope be constructed of transparent fused quartz a reduction in the size efiects another economic saving.

Aside from these advantages resulting from my invention, there are others resulting from a reduction in electrode size. When such electrodes are employed on mercury arcs for the production of light they permit a compactness which especially adapts such an are for use with reflectors. A suitable reflector located behind a mercury arc can greatly enhance the intensity of light falling upon a surface. If the light source is compact and free from appreciable obstructions to -light, the reflector design is greatlysimplified.

My invention, since it enables the employment of electrodes of half to one-third the size of those employed on older arcs of this type, can be moreeasily and. satisfactorily employed in conjunction with reflectors.

Another advantage resulting from the employment of my invention relates to lessened breakage in shipment.-

The vacuum type quartz mercury arc in particular maybe broken in shipment by a mercury slap, whichresults from the heavy mercury metal beingsu ddenly thrown from one endv of the container to' the other. The number of such lamps that'are broken by this cause is in direct proportion to their size and the volume (and hence the weight) of mercury contained therein. My invention permits a reduction of the amount of mercury in these lamps and will therefore result in smaller sized arc tubes.

In the drawing,

Figure 1 represents a'sectional view of an but 'lution,

pere re ationship, the are current decreasing.

as the arc voltage increases, but whose operation. was dependent primarily upon electron emission by substances other than mercury, and in this respect different from the ordinary mercury arc.

The electrodes in this type of lamp contain the alkaline earth oxides such as barium and strontium oxides as their primary active electron emitting substances.

The employment of these substances for the purpose of electron emission is not new as they were used for such purposes as early as 1914. However, the manner in which 'I employ these oxides, and the light source which I obtain by their use I believe to be a novel and distinctive advance in the art of light production.

' This new type of electron emitting electrode for employment in mercury arcs may be made as follows. The alkaline earth oxides ina finely powdered form are thoroughly mixed with granulated 'metallic oxides,

which as metallic hydroxides in aqueous solow by roxyl ion concentration. Typical oxides are ferric oxide, chromic oxide, aluminum oxide, zirconium oxide, nickel oxide,

cobalt oxide, and titanium oxide etc. The proportion of alkaline earth oxide to metal- 110 ox1de-1s dependent upon the design and current duty of the electrode.

This mixture is made into a paste with an organic binder such as cellulose acetate in ether-alcohol solution. The paste is moulded on the lead-in wire which may be tantalum, molybdenum or tungsten; The moulded electrode is dried in a vacuum, and then heated in a-silica tube to about 1000 degrees centigrade to carbonize the binder; and to weld the mass together still further, the electrode is glowed for a few seconds in the oxy-hydrogen reducing flame. The finished electrode is introduced into thev electrode vessel, and the lead- -in wire is'sealed ga tight to the vessel.

'. The weak basic d netallic oxides have been found useful in the construction of these electrodes because of their stability at the operating temperatures (approximately 1100 degrees" centigrade excepting hot spot which is higher temperature) and their give an electrolytic dissociation 'of' ability to adsorb barium and strontium oxide chemical union exists between these substances, and their association in these elech trodes which opcrateat mcandescence should be considered one of adsorption and physical mixture.

The adsorption of the alkaline oxides on the surfaces of the metallic oxides-may be considered analogous to'the adsorption of gases on metallic catalysts in gas reactions such as the ammonia synthesis. The adsorption results in a distorted electron field in the alkaline earth molecule, and when an electricpotential is applied, electrons may be discharged. The electron emission occurs at relatively low temperatures, that is, at room temperature, when the combinations described are employed. These weak basic metallic oxides are employed then as non-volatile supports and as creators of electron emission centers operative at low temperatures.

The completed electrodes are attached to the body of the lamp proper. Two electrodes are sufiicient for either alternating or direct current operation. The assembled lamp is attached to an evacuation and filling system,

and is evacuated. While on the vacuum system, the lamp is heated bythe external application of heat to drive off moisture and gases adsorbed on the walls. Finally the system is cooled on the vacuum and a small quantity of mercury, more than suflicient to supply all the mercury'vapor needed for arooperation, but very little in excess, is admitted.

Since there is too little mercury in the system to permit the establishment of the are by the familiar method of tilting the burner so that mercury can flow from one electrode to the other, short circuiting the system, it is necessary to provide a means for lighting the lamp. This has been accomplished by introducing into the system a small quantity of neon gas at a pressure of a few centimeters.

' If now the arc tube be gently stroked with a cloth to produce an electrostatic charge on the tube, a few neon ions will be formed.

If the two electrodes are maintained.- at' a potential difference greater than 150 volts, 9. gas discharge will be formed which will almost instantaneously volatilize sufiicient mer- 'cury and establish sufficiently high electron emission to permit the mercury arc to establish. The instant that themercury are is started, the voltage drops, and the gas (lischarge ceases to function.

series 'of layers From this point, the gas ceases to play any part in the operation of the are, the arc appearing in every respect to resemble the ordinary mercury arc.

It is essential that during operation that.

of different sizes. The lamp referred to has an arc length about 8 inches.

This lamp is operated and the arc is maintained by the emission from a hot spot on the electrode. Similarly, if the current sup,- ply is interrupted for a very short time, the arc is extinguished, and will not start of its own accord. However, unlike the mercury electrode type, the alkaline earth oxide type cannot be rclighted immediately, for there is not sufiicient emission 'to re-establish the arc in the'mercury, and the vapor pressures within the neighborhood of the electrodes interfere with the action of the inert gas. The lamp must cool before it can be lighted again.

Lamps, such as described, have proven not Thealkaline earth oxides, barium and strontium oxldes, andalso the metallic oxides have thermal. conductivities of the order of 0.0123 calorie per second through, a layer one centimeter deep and an area one square centimeter for an increase in temperature of one degree centigrade. This means that they are even poorer conductors of heat than mercury. There is the-characteristic hot spot from which the electrons are emitted. In this instance there is not any mercury at the electrode to evaporate.

All thehcat energy generated must be dissipated from 'the electrmle itself. The electrode therefore liecomes very warm, and volati'lization of the alkaline earth oxides becomes aresult. Whereas the volatilization of appreciable mercury from the mercury type of electrode is without serious consequences, any appreciable volatilization of the alkaline earth oxides will result in greatly shortened useful life.

At the time'the electrode is moulded, a gif metal gauzes, foils, or spirals of metals which have high thermal conductivity areintroduced into the mass. These metals may be tungsten or molybdenum.

rod

These layers or spirals are connected and 'trode to the'walls which in turn may cooled by any familiar method, such as metal 5 cooling vanes.

Referring to the drawing, there is shown an electrode mass 2 which is made from-a mixture of alkaline earth oxides and metallic oxides, as hereinbefore explained. The alkaline earth oxides -may be of barium or strontium; and .the typical metallic oxides are ferric oxide, aluminum oxide, nickel oxide, cobalt oxide, etc. The electrode mass 2 has layers of metallic gauze 3 distributed therein, and contacting with the wall of a silica sleeve 1 surrounding the electrode. The sleeve 1 is sealed to the electrode vessel 5, the latter carrying a quantity 6 of mercury between its wall and the wall of the sleeve. A lead-in wire 4 is sealed into the electrode vessel and embedded in the electrode mass 2.

Employing electrodes constructed in accordance with my invention, it is possible to construct mercury arc lamps for the production of visible and ultra violet light and for current rectification which compare in electrical andradiation characteristics comparable to the familiar mercury electrode types of arcs and which have some advan tages not enjoyed by the older type of arc. Thus the lamp may be operated directly on alternating current by applying potential to two electrodes only whereas the ordinary mercury arc requires three electrodes for such operation. The very small quantity of mercury in the new lamp enables the lamp to be operated in any position, and also results in ease of shipment.

Having thus described my invention, what I claim'as new and desire to secure by Letters Patent, is:

1. An electrode for vapor electric devices, comprising a gas tight vessel, an electrode mass formed .of alkaline earth oxide intimately mixed with weakly basic metallic oxides, a sleeve surrounding said electrode mass, and a plurality of pieces of metal dis tributed throughout the electrode mass and contacting thewall of the sleeve, said metal pieces being of higher thermal conductance than the electrode mass to conduct aportion of the heat of the electrode mass to the wall of the sleeve.

2. An electrode for vaporelectric devices,

. comprising a gas tight vessel, an electrode mass formed of barium and strontium oxides intimatel mixed with particles of the oxides of IIOII, c romium, aluminum, nlckel, cobalt,

3. In an electrode for vapor electric de- I vices, an electrode mass formed of alkaline earth oxides and metallic oxides, a sleeve surrounding said electrode mass, and a plurality of pieces of metal gauze distributed throughout the electrode mass and contacting the sleeve to conduct heat from the electrode mass to the sleeve.

'4. An electrode for vapor electric devices, comprising a gas tight vessel, an electrode mass formed of alkaline earth oxides and metallic oxides, a lead-in wire sealed into the vessel and embedded in the electrode mass, a sleeve surrounding the. electrode mass and sealed to the vessel, and pieces of metal distributed throughout the electrode mass and contacting the sleeve to conduct heat from the electrode mass to the sleeve.

5. In a vapor electric devi tight vessel containing a sma quantity of mercury, and a rare gasfor the purpose of establishing the mercury arc, an electrode comprising an electrode mass formed of alkaline earth oxides and metallic oxides, a leadin wire sealed into the vessel and embedded in the electrode mass, a sleeve surrounding the electrode mass and sealed to the vessel, and pieces of metal distributed throughout the electrode mass and contacting the sleeve to conduct heat from the electrode mass to the sleeve.

This specification signed this February, 1932. WILLIAM T. ANDERSON, JR.

zirconiunn titanium and zinc, a lead-in wire of metallic tungsten sealed into the vessel and embedded in the electrode mass, a sleeve surrounding the electrode mass and sealed to -the vessel, and pieces of tungsten metal gauze distributed throughout the electrode mass,

29th day-of aving a gas 1 

